Method for straightening and for relieving stresses in workpieces



May 30, 1961 G. H. APPEL 2,935,956

METHOD FOR STRAIGHTENING AND FOR RELIEVING STRESSES IN WORKPIECESOriginal Filed Jan. 12, 1956 Ger/lard if aqp vel Wm W dtarngy:

United States Patent O METHOD FOR STRAIGHTENING AND FOR RELIEVINGSTRESSES IN WORKPIECES Gerhard H. Appel, Windsor, Ontario, Canada,assignor to Appel Process, Ltd., Windsor, Ontario, Canada, a company ofCanada Original application Jan. 12, 1956, Ser. No. 558,750,

now Patent No. 2,894,421, dated July 14, 1959. Divided and thisapplication Dec. '10, 1956, Ser. No. 627,446

6 Claims. (Cl. 29-544) This application is a division of a priorapplication, Ser., No. 558,750 of January 12, 1956, now Patent No.2,894,421 of July 14, 1959, directed to apparatus.

The invention relates to a new method for relieving longitudinalstresses in elongated workpieces by cold forging.

An elongated workpiece is fed axially and intermittently in smallincrements through an annular set of hammers or forging dies with theworkpiece being held at its trailing and leading ends in axial alinementwith the throat of the dies. These impart, in off-beat relation to thefeeding of the workpiece, a series of sharp, rapidly delivered hammerblows which reduce the increments to a plastic condition and thusrelieve them of longitudinal stresses.

With the leading end held and guided to travel axially of the travelthrough the throat, the leading end, already plasticized and thusrelieved of longitudinal stress, is not again subject to such stress.

With the line connecting the held and guided leading end, and the diesthroat being a straight line, the work piece will also be straightened.

Other objects and advantages of the invention will become apparent fromthe following detailed description of the method and a preferred form ofthe apparatus for carrying it out as illustrated in the accompanyingsingle figure of drawings.

The drawing is a partly sectioned, fragmentary plan view of a coldforging machine equipped with apparatus embodying the features of theinvention and particularly adapted for carrying out the newstraightening and stress relieving method.

For purposes of illustration the apparatus for carrying out theinvention has been shown in a form adapted for application to aparticular type of cold forging machine. It is to be understood,however, that this is merely exemplary and that the method may becarried out by other means or apparatus or in conjunction with coldforging or swaging machines other than the specific machine illustrated.

Referring to the drawing, the apparatus shown is adapted to carry outthe new straightening and stress relieving method in cooperation with acold forging machine of the type disclosed in the co-pending Appelapplication, Serial No. 450,500, filed August 17, 1954. It will beappreciated, however, that the method can be carried out in cooperationwith other types of forging or swaging machines. Insofar as it conernsthe present invention, the machine comprises a metal working tool unitor rotary die set 1 supported on a frame member 2 connected to otherelements of the machine structure by spaced parallel tie rods 3. The tierods support and guide a head 4 for linear translation toward and fromthe tool unit. Any suitable drive means may be utilized for translatingthe head. As shown in the drawing, the head 4 carries a chuck 5 adaptedto grip and support one end of a workpiece such as the metal tube W. Thechuck ice is rotated relatively slowly as the head advances to feed theworkpiece axially through the tool unit 1.

The tool unit or die set 1 comprises a plurality of hammers of a dieelement 6 arranged in an annular series and supported for radialmovement toward and from the workpiece which is fed coaxially throughthe set. It will be understood that the inner or work-engaging ends ofthe die elements are shaped to form the work to the desired externalcontour which may be round, or any other desired shape. In the case ofthe tubular workpieces, the internal shapes and dimensions aredetermined by a suitable mandrel 7' disposed within the workpiece withinthe area engaged by the die elements. In the exemplary machine themandrel is carried at the end of the mandrel supported rod 8 extendingback through the chuck 5 to the interior of the machine.

In operation, the chuck 5 and the workpiece W are rotated while the head4 advances intermittently and in olfbeat relation to the strokes of thedies to feed the workpiece axially through the die set. During such feedthe hammers or die elements 6 are actuated intermittently and inofi-beat relation to the feed to impart sharp, rapidly delivered hammerblows to the limited section or increment of the workpiece between thedies. The actuating mechanism may be of any preferred character and isusually arranged so that oppositely disposed hammers act simultaneouslyin delivering their hammer blows to opposite sides of the workpiece.

In straightening and relieving longitudinal stresses in accordance withthe improved method, the leading end of the workpiece W as it emergesfrom the die set 1 is firmly engaged and rigidly held in coaxialalinement with the throat of the die set. It is also desirable althoughnot essential to the attainment of the desired result, that the end ofthe workpiece supported by the chuck 5 be precisely alined with the dieset. Any tendency of the workpiece to elongate more at one side than theother and thus to bend or twist transaxially is counteracted by theaction of the die elements which plasticize and force the material andforce it into precise axial alinement with the support at the reducedend of the workpiece. This, of course, develops longitudinal stressesalong the entire length of the workpiece but those stresses arecompletely relieved when the material becomes plastic under the dies.Thus, the compensation for the conditions which produce the tendency tobend is elfected within the area where the metal is temporarilyin aplastic condition and therefore the redistribution of metal required forthe production of a straight workpiece is effected without thedevelopment of any stresses in the workpiece. In the case of tubularworkpieces, this redistribution of metal results in substantialequalization of the wall thickness throughout the entire length of theworkpiece. Accordingly, by use of the new method, a straight,stress-free workpiece and therefore a better product is produced in asingle operation and with material saving in production costs.

Any suitable means may be utilized for supporting the workpiece W uponits emergence from the die set. Thus, the support may comprise a seriesof stationarily supported members engageable with the workpiece atcircumferentially spaced points to provide lateral support whilepermitting axial movement of the workpiece which finally is pushedthrough the metal working tool set and emerges as a finished productfrom the rear of the machine. Alternatively, the support may be arrangedto grip the leading end of the workpiece and to move with it in a pathpre 3 ward end by a plug 13. A socket 14, shaped and dimensioned toreceive the end of the workpiece W with a tight gripping fit, isprovided centrally of the plug.

In the particular machine illustrated a cylinder 11 is rotatablysupported within a tubular liner 15 as by bearings 16. The liner isfitted into a rigid sleeve member 17 suitably secured to the framestructure of the machine. As herein shown, the sleeve is seated in anaperture 18 in the frame member 2 and is formed with a flange 19 adaptedto abut the inner wall of the frame member and hold the sleeve againstthe axial movement. In this instance the sleeve also provides supportfor the die set 1 which is mounted on and secured to the forward end ofthe sleeve in any suitable manner.

The cylinder 11 is secured against the endwise move ment relative to theliner 15 by a collar element 20 which permits rotation of the cylinderwith the piston and the workpiece supportcd'thereby. A port 21 in thesleeve and liner provides for admission of fluid coolant to the spacebetween the cylinder and the liner, the coolant being discharged througha port 21' in the collar 20. Pressure fluid such as compressed air isadmitted to the aft end of the cylinder by way of a port 22 in the endwall of the cylinder. Thus, by directing compressed air through the port22, the piston 10 may be driven toward the forward end of the cylinderto impose a yieldable resistance to the advancing workpiece through thedie set.

At the beginning of a forging operation, compressed air admitted to thecylinder 10 through the port 22 holds the piston 10 at the forward endof the cylinder closely adjacent the die set 1. The workpiece Wtherefore enters the socket 14- irnmediately on emerging from theforging dies. A substantial pressure as, for example, 50 p.s.i., ismaintained in the cylinder as the forging operation proceeds, thusapplying a yielding force to the piston counter to the feed of theworkpiece. This effectually keeps the workpiece firmly seated in thesocket and therefore coaxially alined with the die set through itsentire length. The piston is forced back into the cylinder as theworkpiece advances through the die set.

T o facilitate disengagement of the workpiece from the socket 14- thepiston is provided with a pressure actuated plunger 23 adapted to beprojected into the socket 14 from its inner end. The plunger 23 as shownis formed with a cylindrical head 24 extending through an opening at theend wall of the piston. A flange 25 adjacent the forward end of the headlimits rearward movement of the plunger.

Upon completion of the forging operation the head 4 and the chuck areretracted in the" usual manner with the dies preferably opened up toatford clearance for withdrawal of the work. The support piston '10,being subjected to the pressure in the cylinder, moves along with thework until it reaches the end of the cylinder. The pressure on the head24 acts to advance the plunger 23 and push the workpiece from thesocket. Upon its withdrawal from the die set, the workpiece may bereleased from the chuck and removed from the machine.

It will be apparent from the foregoing-that the novel straightening andstress relieving method provided by the invention materially. improvesthe product produced by cold forging and swaging operations. Thefinished workpiece produced by this method is precisely straight andcompletely free of bending stresses. In the case of tubular workpieces,the walls are more nearly of uniform thickness. Furthermore, productioncosts are reduced since a number of supplementary operations heretoforerequired are eliminated. While the new method can be carried out invarious ways and with different types of equipment, the inventionprovides simple and efficient apparatus for that purpose which is easyto operate and which is readily applicable to conventional cold forgingor swaging machines.

I claim as my invention:

1. In a method for cold forming an elongated, rodlike, metal work-piece,whether hollow or solid, comprising simultaneously applying to thesurface of a minute increment of the metal workpiece at leastthree,radially arranged, inwardly directed, equally spaced, equal and opposedpressures engaging and substantially completely girdling the workpiece;in such method, that improvement which comprises applying the pressuresto the workpiece by at least three radially arranged pressure applyingdies providing a die throat, with each die subjected to two opposing,equal, transverse forces, each of which transverse forces has atransverse component and a radial component, the transverse componentsbeing directed so that they are equal and opposite and thus balancethemselves out, leaving only a net radial resultant directed along anextension of the radius of the workpiece and towards the central axis ofthe workpiece so that each force on a die which applies pressure to theworkpiece is truly radial to the workpiece and has no unbalancedtransverse components; the method further including axially push feedingthe workpiece through the throat of the dies and engaging the leadingend of the workpiece immediately as it emerges from the throat of thedies and holding and guiding such end thereafter in precise axialalinement with the axis of push-feed while the workpiece is push fed.

2. In a method for cold forming an elongated rod-like metal workpiece,whether hollow or solid, which method comprises applying to each of manylongitudinal adjacent minute increments of a metal workpiece, insuccessive steps, so as to extend over substantially its entire exteriorsurface, at least three, radially arranged. inwardly directed, equallyspaced, equal and opposed and simultaneously applied pressures engagingand substantially completely girdling the workpiece; in such method thatimprovement which comprises applying the pressures to the workpiece byat least three radially arranged pressure applying dies providing a diethroat with each die subjected to two opposing transverse forces, thetwo up posing transverse forces being so directed that their transversecomponents are equal and opposite and thus balance themselves out,leaving only a net radial resultant of the two forces, so that eachforce on a die which applies pressure to the workpiece becomes trulyradial and has no unbalanced transverse components, and so that thepressures on the workpiece applied by each pressure applying die arebalanced out by equal and opposite pressures applied by the remainingpressure applying dies; the method further including axially pushfeeding the workpiece through the throat of the dies and engaging theleading end of the workpiece immediately as it emerges from the throatof the dies and holding and guiding such end thereafter in precise axialalinement with the axis of push-feed while the workpiece is push fed.

3. A method for cold forming an elongated metal workpiece, hollow orsolid, having a central axis, comprising the steps of surroundingsubstantially the entire outer peripheral surface of a single axialincrement of the workpiece with at least three opposed dies providing adie throat, each die arranged radial relative to the workpiece centralaxis; simultaneously loading all of the dies by subjecting each of themto two equal and opposing forces which are transverse relative to thedie axis and which are so arranged as to balance out all transversecomponents of said two opposing forces and leave only a radial resultantwhich radial resultant is directed towards the workpiece central axisalong the die axis; whereby the resultant load on each die is radial andhas no unbalanced transverse components, and with the said radialresultant on each die being equal to the radial resultant of every otherdie; moving the dies under the influence of their respective radialresultant loads into engagement with the workpiece increment fortransmitting the respective resultant loads to the workpiece and therebyapplying pressure to the workpiece for forming it; the method furtherincluding axially push feeding the workpiece through the throat of thedies and engaging the leading end of the workpiece and holding andguiding such end thereafter in precise axial alinement with the axis ofpush-feed while the workpiece is push fed.

4. A method for cold forming a metal workpiece, hollow or solid, whichis elongated and rod-like in shape and thus has an elongated centralaxis, said method employing at least three pressure applying dies whichare equally spaced on workpiece radii circumferentially around theperiphery of the workpiece in a plane normal to its axis and which diesgirdle the workpiece and are movable towards and away from the axis,said dies providing a die throat, said method further comprisingrepeated identical cycles of steps with each cycle including the diesengaging and acting on a small axial increment of the workpiece and witheach cycle comprising the steps of gradually and simultaneously movingall of the dies equal minute distances inwardly towards the workpieceaxis inwardly of the workpiece surface and under equal loads whereby thedies gradually squeeze the workpiece increment then worked upon untilthe metal in that workpiece increment flows and the periphery of thatworkpiece increment assumes the shape of the die faces engaging theworkpiece; then stopping the inward movement of the dies and holding thedie loads for a short time; and then retracting the dies away from theworkpiece axis; and then moving the workpiece axially through the diesto present a succeeeding increment of the workpiece to the dies; andrepeating the cycles until all increments of the workpiece from one endto the other have been successively engaged and formed by the dies; insuch method, that improvement which comprises applying the pressures tothe workpiece by subjecting each of the dies to two opposing transverseforces each of which forces have transverse components and radialcomponents and with their transverse components being so directed thatthey are equal and opposite and balance themselves out leaving only anet radial resultant so that each force on each of the dies, whichapplies pressure to the workpiece, is truly radial and has no net orunbalanced transverse components; the method further including axiallypush feeding the workpiece through the throat of the dies and engagingthe leading end of the workpiece and holding and guiding such endthereafter in precise axial alinement with the axis of push-feed whilethe workpiece is push fed.

5. A method for cold forming an elongated metal workpiece, hollow orsolid, having a central axis comprising numerous identical cycles ofsteps, with each successive cycle acting upon a successive single axialincrement of the workpiece, each cycle comprising essentially the stepsof surrounding substantially the entire outer peripheral surface of asingle axial increment of the workpiece with at least three opposedpressure applying dies which are arranged radially relative to theworkpiece axis to provide a die throat; simultaneously loading all ofthe dies and moving them under the influence of their loads towards andinto pressure applying engagement with the workpiece, with the movementof each of said dies being only in the direction of a single radius ofthe workpiece, with the load on each of the dies being formed of aradially directed resultant force directed only in the same direction asthe respective single radius which defines the direction of movement ofthat die, and also being formed of pairs of non-radial force componentswith each non-radial force component of each pair being equal to andopposite to and counterbalancing and cancelling out the other non-radialforce component of that pair and with the radially directed resultantforces of each of the dies being equal to one another; holding the diesin a pressure applying engagement with the workpiece for apre-determined time for forming the workpiece increment; then releasingthe loads simultaneously and retracting the dies from the workpiecealong the same path in which they moved towards the work-piece; themethod further including axially push feeding the workpiece through thethroat of the dies and engaging the leading end of the workpiece andholding and guiding such end thereafter in precise axial alinement withthe axis of push-feed while the workpiece is push fed.

6. A method for cold forming a metal workpiece having a central axiscomprising loading substantially the entire outer periphery of a singleincrement of the workpiece with forces that are inwardly directed andwhich resolve into force components which are either radial to theworkpiece axis or are normal to radii of the workpiece and tangent to ahypothetical circle whose axis is the axis of the workpiece; and withall of the radial force components being in balance at the axis of theworkpiece and with each of said normal force components being balancedby another equal and opposite normal force component; there being noforces at any time which do not resolve into truly radial components ornormal-to-radii components; said loading being characterized by beingrapidly applied and removed in a uniform time pattern; applying theloading to successive increments of the workpiece; and changing theincrements upon which the loading is applied during the load removedtime of the loading time pattern; the method further including axiallypush feeding the workpiece through a throat of dies which provide theforces and engaging the leading end of the workpiece immediately as itemerges from the throat of the dies and holding and guiding such endthereafter in precise axial alinement with the axis of push-feed whilethe workpiece is push fed.

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